Author: Robert Hyatt
Date: 08:43:38 09/24/98
In the ICCA Journal, Vol. 16, No. 4, GM Timoshchenko is comparing various
chess programs on how they evaluate bishops vs knights. He gives several
positions, with this one being the most interesting at present:
+---+---+---+---+---+---+---+---+
8 | | | | | | | *K| |
+---+---+---+---+---+---+---+---+
7 | *P| *B| | | *B| *P| *P| |
+---+---+---+---+---+---+---+---+
6 | | | | | *P| | | *P|
+---+---+---+---+---+---+---+---+
5 | | | | | | | | |
+---+---+---+---+---+---+---+---+
4 | | | | | | | | |
+---+---+---+---+---+---+---+---+
3 | | | N | | P | N | | P |
+---+---+---+---+---+---+---+---+
2 | P | | | | | P | P | |
+---+---+---+---+---+---+---+---+
1 | | | | | | | K | |
+---+---+---+---+---+---+---+---+
a b c d e f g h
fen: 6k/pb2bpp1/4p2p///2N1PN1P/P4PP/6K/ w - -
Here is the gist... to feed this to a program and with no searching,
see how it evaluates this. Chessmaster 2100 says -.26, Fritz-2 says -.47,
and chess-genius 1.0 says -.48. I recently fixed two "holes" in Crafty's
evaluation, one concerning "if you have one bishop in the ending, get your
pawns on the *other* color squares" and the other "if in an endgame, with
pawns on both wings, a bishop is significantly better than a knight."
This last influences the evaluation of the above position quite markedly,
because this is an endgame, and black is going to get the bishop-over-
knight in endgame bonus two times since black has two bishops, white has
none. Black also gets the traditional bishop-pair bonus as well, which
might or might not be overkill here. In any case, I first gave this to a
GM to look at and the response "black wins easily." Not surprising, the
bishop pair vs the pair of knights should favor the bishops. I then told
him that Crafty "statically" evaluates this position as "-.93" which is
the raw score Evaluate() returns here. He said "hmmm... ". And we had
an interesting conversation without concluding whether this is too large,
too small, or "just right."
I have three scoring terms that are producing this -1 pawn advantage for
black here: the bishop pair bonus is .25 (1/4 pawn). The bishops get
a bigger bonus for "mobility" than the knights, and these bishops are
monsters, having almost an open board to roam around, and then my new
"bishops are better than knights in endings with pawns on both sides of
the board" which is .3, but since there are two bishops, this adds up to
.6
Any comments on this position? There are a total of 5 of these
interesting positions in the journal article. One with single B vs
N:
+---+---+---+---+---+---+---+---+
8 | | | | | | | *K| |
+---+---+---+---+---+---+---+---+
7 | *P| | | | *B| *P| *P| |
+---+---+---+---+---+---+---+---+
6 | | | | | *P| | | *P|
+---+---+---+---+---+---+---+---+
5 | | | | | | | | |
+---+---+---+---+---+---+---+---+
4 | | | | | | | | |
+---+---+---+---+---+---+---+---+
3 | | | | | P | N | | P |
+---+---+---+---+---+---+---+---+
2 | P | | | | | P | P | |
+---+---+---+---+---+---+---+---+
1 | | | | | | | K | |
+---+---+---+---+---+---+---+---+
a b c d e f g h
fen: 6k/p3bpp/4p2p///4PN1P/P4PP/6K/ w - -
score: -.22
one with B+R vs N+R (testing the hypothesis that B+R is better than
N+R:
+---+---+---+---+---+---+---+---+
8 | | | | | | | *K| |
+---+---+---+---+---+---+---+---+
7 | *P| | *R| | *B| *P| *P| |
+---+---+---+---+---+---+---+---+
6 | | | | | *P| | | *P|
+---+---+---+---+---+---+---+---+
5 | | | | | | | | |
+---+---+---+---+---+---+---+---+
4 | | | | | | | | |
+---+---+---+---+---+---+---+---+
3 | | | | | P | N | | P |
+---+---+---+---+---+---+---+---+
2 | P | | | R | | P | P | |
+---+---+---+---+---+---+---+---+
1 | | | | | | | K | |
+---+---+---+---+---+---+---+---+
a b c d e f g h
fen:6k/p1r1bpp/4p2p///4PN1P/P2R1PP/6K/ w - -
score: -.19
(I don't recognize B+R as better. I used to, but didn't like the
result, because with pawns on one side of the board, often the knight
seemed to actually help more than the bishop because the bishop is
locked on one color.)
Then B+Q vs N+Q, testing the hypothesis that N+Q is better than
B+Q (again, I don't recognize this either, yet).
+---+---+---+---+---+---+---+---+
8 | | | | | | | *K| |
+---+---+---+---+---+---+---+---+
7 | *P| | *Q| | *B| *P| *P| |
+---+---+---+---+---+---+---+---+
6 | | | | | *P| | | *P|
+---+---+---+---+---+---+---+---+
5 | | | | | | | | |
+---+---+---+---+---+---+---+---+
4 | | | | | | | | |
+---+---+---+---+---+---+---+---+
3 | | | | | P | N | | P |
+---+---+---+---+---+---+---+---+
2 | P | | | Q | | P | P | |
+---+---+---+---+---+---+---+---+
1 | | | | | | | K | |
+---+---+---+---+---+---+---+---+
a b c d e f g h
fen: 6k/p1q1bpp/4p2p///4PN1P/P2Q1PP/6K/ w - -
score: -.19
and finally a B+B vs B+N:
+---+---+---+---+---+---+---+---+
8 | | | | | | | *K| |
+---+---+---+---+---+---+---+---+
7 | *P| *B| | | *B| *P| *P| |
+---+---+---+---+---+---+---+---+
6 | | | | | *P| | | *P|
+---+---+---+---+---+---+---+---+
5 | | | | | | | | |
+---+---+---+---+---+---+---+---+
4 | | | | | | | | |
+---+---+---+---+---+---+---+---+
3 | | | | | P | N | | P |
+---+---+---+---+---+---+---+---+
2 | P | B | | | | P | P | |
+---+---+---+---+---+---+---+---+
1 | | | | | | | K | |
+---+---+---+---+---+---+---+---+
a b c d e f g h
fen: 6k/pb2bpp1/4p2p///4PN1P/PB3PP/6K/ w - -
score: -.69
(all scores are from Crafty, no search, just a call to the
Evaluate() procedure with the given position set up...
Comments welcome... Bob
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